This allele is a derivative of Mybpc3tm1Jse. Mutant animals were mated to Tg(EIIa-cre)C5379Lmgd to delete the PGK-neo cassette, leaving behind a 97 bp residual loxP sequence within exon 30. The resulting mutant allele generates a transcript that skips the 5' half of exon 30 and that encodes a peptide that is 30 amino acids shorter than the wild-type peptide and contains 166 novel amino acids.